Cover the bottom of a heavy pot with olive oil and heat over medium heat. Lay eggplant slices in the bottom and let them soak up oil until they are yellow (darkened) and soft, 3-4 minutes. Remove the slices to a plate and add more to the pot. Add more olive oil as it is drunk by the eggplant. When the eggplant is done, add the onion to the pot and cook until golden. Add all ingredients to the pot, stir together, and cook over medium-low heat, stirring occasionally, for two hours or until the vegetables are soft and melt in the mouth.